Monday, February 16, 2015

NEW
YORK (GenomeWeb) – Penguins appear to lack taste receptor genes
governing three of the five tastes, according to a genomic analysis
conducted by a trio of researchers from the US and China.

The trio, led by Jianzhi Zhang at the University of Michigan, searched through the genomes of the Adélie penguin (Pygoscelis adeliae) and emperor penguin (Aptenodytes forsteri)
and other birds for taste receptor genes. Penguins, they found, lacked
receptors involved in perceiving sweet, bitter, and umami taste, but
have retained salty and sour taste receptors, as they reported in Current Biology.

"Penguins
eat fish, so you would guess that they need the umami receptor genes,
but for some reason they don't have them," Michigan's Zhang said in a
statement. "These findings are surprising and puzzling, and we do not
have a good explanation for them. But we have a few ideas."

Zhang
and his team searched for genes that encode taste receptors — sour's
PKD2L1, salty's ENaC, umami's Tas1r1–Tas1r3 heterodimer, sweet's
Tas1r2–Tas1r3 heterodimer, and bitter's Tas2r genes — in Adélie and
emperor penguins, as well as in the little egret and a dozen or so other
birds whose genomes were publicly available.

None of
the birds had the Tas1r2 gene, which encodes part of the sweet taste
receptor, though the researchers did find the gene in mammalian and
reptile outgroups.

Tas1r3, which makes up the other
part of the sweet taste receptor heterodimer as well as part of the
umami taste receptor heterodimer, was also lacking in penguins. It was,
the researchers noted, present in other birds.

The
other half of the umami taste-specific receptor, Tas1r1, is actually a
pseudogene in penguins, the researchers found, as it contains a two
basepair deletion that leads to a premature stop codon.

Other penguin species shared this pseudogene, but other birds have working copies, Zhang and his team reported.

Similarly,
the researchers identified three Tas2r pseudogenes in penguins while
most other birds had working copies of the gene behind bitter taste.
They noted, though, those three penguin pseudogenes were orthologous to
the two working copies and one pseudogene version of Tas2r found in the
little egret.

This, Zhang and his colleagues said,
indicates that the common ancestor of all penguins lost the umami and
bitter tastes, while the sweet taste was lost even earlier in the avian
lineage.

The receptor gene for sour taste was present
in all birds, including penguins, as were the genes encoding the
subunits of the salty taste receptor, ENaC.

Zhang and
his colleagues said they suspect that the penguin's ancestral stomping
grounds of Antarctica might have had a role in this gene loss.

Trpm5,
which is involved in transducing the sweet, umami, and bitter tastes,
doesn't work well at lower temperatures. At freezing temperatures, the
researchers suggested that it might not work at all, leading to the
inability to taste sweet, umami, and bitter, and then to the loss of the
genes linked to those tastes.

Tuesday, February 10, 2015

When yellow-eyed penguins arrived in New Zealand just decades
after the country's native waitaha penguin became extinct, it
became one of the most rapid prehistoric animal turnovers
ever found, University of Otago researchers say.

The team of researchers used carbon dating and DNA analysis
of penguin remains from coastal New Zealand to establish the
timing of the waitaha's extinction and the colonisation by
yellow-eyed penguins from the subantarctic.

University of Otago postdoctoral research fellow Dr Nic
Rawlence, who carried out the study, said the combination of
ecology, archaeology and DNA in this way was new and was also
being used to investigate if similar patterns exist with New
Zealand sea lions, Stewart Island shags, elephant seals and
fur seals.

Previous research had shown at the time of human arrival, New
Zealand was inhabited by the waitaha penguin. ''Hunting and habitat change apparently caused the extinction
of this unique mainland penguin, before the yellow-eyed
penguin later arrived here from the subantarctic,'' Dr
Rawlence said.

The new dating study showed waitaha went extinct around the
same time as the giant flightless moa, within 200 years of
Polynesian settlement of New Zealand - before 1500 AD. The
yellow-eyed penguin then replaced the extinct penguin within
about 20 to 30 years, in the early 1500s. ''It's one of the most rapid biological turnovers ever
documented.''

Associate Prof Ian Smith, who was also involved in the study,
said the very rapid biological shift implied a substantial
change in human pressure around that time. ''Interestingly, recent archaeological studies similarly
suggest that the Maori population in southern New Zealand
declined around 1500 AD, and coincided with a major dietary
shift.''

Dr Rawlence said if there had not been the dietary shift from
large animals to fish and shellfish, yellow-eyed penguins
would not have been able to fill the niche left by the
waitaha. ''Yellow-eyeds would have arrived and then become extinct if
there hadn't been that change.''

The near absence of the yellow-eyed penguin from the mainland
before the extinction of the waitaha was similar to what
happened to New Zealand's sea lions.

A University of Otago study published last year found today's
sea lions replaced an extinct prehistoric New Zealand sea
lion. The Marsden and Allan Wilson Centre-funded research on
penguins included team members from the Universities of
Auckland, Otago, Adelaide and Oslo, as well as Canterbury
Museum and Te Papa.

The team's findings were published this week in the leading
international journal Quaternary Science Reviews.